Process for making color half-tones.



PROCESS FOR MAKING COLOR HAL'F TONES BROWN,

APPLICATION FILED JULY 13, I9I6.

Patented Apr. 23, 1918.

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PROCESS FOR MAKING: COLOR HALF TOlNES Specification of Letters Patent.

Patented Apr. 23, lFild.

Application filed July 18, 1916. Serial No. 109,948.

.722 all whom it may concern."

Be it. known that l, HowARo THoMAs BROWN, a citizen of the United States,'re-

siding at Los Angeles, in the county of Los Angeles and State of California, have invented new and useful Impro ements in Processes for Making Color Half-Tones, of which the following is a specification.

This invention relates to a process for making color half tones, and pertains especially to a process suitable for use inprinting colored pictures for newspapers, whereby photographs, oilpaintings, wash drawings and the like may be reproduced in natural color efl ects.

It is an object of this invention to provide a process for producing engravers plates for printing pictures in colors, and the primary feature of this invention consists in the process whereby a half tone negative is prepared and portions thereof stopped out j for printing therefrom an engravers plate dill for each of the colors used in printing. V

In addition to the primary features of this invention there are certain specific steps in the process by which ease of manipulation and edectiveness in the completed picture is secured.

The embodiment of myinvention as described herein comprises reproducing a picture by means of the three basic colors, blue, red and yellow, but the invention is not limited to these colors, as others may be used.

Figure l is a view of a half tone negative. 9 shows the strip for reducing the tone values.

Fig. 2 is the black and white negative.

Fig. 3 is the key negative which is produced by placing the black andwhite negative over the half tone negative.

Fig. l is the key plate produced from the key negative;

Fig. 5 is a tracing negative produced by placing a transparent film over the key negative, thereby providing a surface upon which pigment may be applied to block out the various portions of the picture.

Fig. 6 is the tracing negative with the foliage of the trees blocked out to produce a red color negative.

In the carrying out of this process the op erator or artist must'understand the com osition of colors. With-the basic colors, b ue,

.posed of blue,,red and yellow, and other secondary colors would be composed of combinations of two or more of the basic colors. For example, with the color compositions just described, when it is desired to print objects which are green, such as grass, provision must be made on the blue plate for printing blue for the grass, and provision must be made on the yellow plate for printing yellow for the grass, one color being printed over the other.

The specific steps in the embodiment of the process described herein consists in first making a half tone negative 7 of the copy preferably in the usual manner, that is, by placing a screen in front of the plate when the latter is exposed. In my process I prefer using wet plates made by the collodion process. The plates are made by Howing negative glass with collodion and sensitlzing the collodion by dipping into a silver bath, then exposing the plates. A contrasty black and white negative 8 is also made by making an exposure ofthe same copy with the half tone screen removed. The half tone and the black and white negatives are coated with rubber and collodion, thereby providing a film which may be stripped from the plate. The half tone negative is then stripped from the plate and is placed in the desired position upon a glass lay out plate. The whole plate is then coated with collodion in order to protect the lay-out from damage by water or other injury which may occur during the carrying out of the process. This half tone portion of the lay-out lolackand white negative strip over the half tone negative and maintains itthere in registry while a transfer is made to the metal engravers plate, but permits'easy removal of the same. The negative produced by superimposing the black and white negative over the half tone negative is hereinafter called a key negative, and the engraversplate produced therefrom is hereinafter called a key plate. This key plate is used to reproduce the black and deeper tones in the printed picture, light tones being eliminated therefrom.

After the key plate has been printed from the key negative the black and white negative is stripped off the half tone negative.

is is easily effected by reason of the character of the cement. A transparent film is now made by flowing a negative glass with a vehicle, preferably sensitivecollodion, then dipping in a silver bath. After the emulsion so formed is well sensitized, it is rei. moved and washed with water without a brush this is app exposure to the light. After thoroughly washing, it is cleaned off with a fixing agent, preferably a strong solution of potassium cyanid and again washed. The film is now dried and coated with rubber and collodion to produce a flexible working film. This working film is used as a tracing film. The film is then stripped from the glass and superimposed upon the half tone negative with the side which was next to the negative glass turned outwardly, thus exposing the film side for workin upon. This provides a working surface (t e side which was next to the negative glass) which is slightly roughened and possibly contains a slight deposit of silver iodid. Such surface will take the pigment which is afterward applied and does not require a thick' coating of the same. The negative so produced is hereinafter called a tracing negative, and is used for making each of the color negatives from which are printed the engravers plates.

A blue color negative is made by stopping out the portions of the tracing negative which do not have blue ,as an element of the color composition. This is preferably done in the following manner: A soluble gum is made with red or yellow pigment, and with ied to the portlons of the plate which are to be eliminated. In mak- 1ng the blue color negative the parts which 7 are to be straight blue such as the water and sky, parts which are to be green, such as grass and foliage of trees, and other parts having blue as an element would not be stopped out. Thus, the purple colored distant mountains and shadows .of rocks would haveblue as an element, and also the brown parts, such as tree trunks, etc. After making the transfer to the engravers plate thepigment is. washed from the tracing negative and the latter is ready for treatment to produce a red plate.

The portions of the plate which do not contain red as an'element are stopped out by blocking out with the pigment solution dirt, hillsides, he n ire thick layers to as in the blue plate. In addition to the straight red tones the portions such as distant mountains and shadows of rocks, the brown portions-such as tree trunks, dirt and hillsides, would not be stopped out. The resulting color negative is used for producing the red plate. A transfer is made to engravers metal, producing an engravers red late.

T e next plate'to be made is a yellow plate. The same process is followed as in the blue and red plates. The tracing negative is washed to remove the pigment and the portions of the negative which do not contain yellow as an element are stopped out. The portions which contain yellow besides the straight yellow may be green, such as the grass and foliage of trees, and brown such as tree trunks, dirt and hillsides. A transfer is made from this plate to engravers. metal, thereby producing a yellow printing plate.

The strength of the different tone values in the different color plates may be reduced in the following manner: A system of parallel lines is ruled on white paper. Areduction is then made so that the parallel lines will correspond with the half tone used. For illustration, if a sixty-five line screen is used for making the half tone, the lines should be reduced so that there are sixtyfive to the inch. A positive is now made of the same, showing white lines and a black back-ground. This positive is placed over the'portion of the half tone to be reduced, it being placed with the lines at right angles to the line of the screen of the half tone negative. The surplus not desired may be removed from the negative by cutting with a sharp knife thereby leaving upon the negative a portion which exactlv conforms 1n shape to the area to be reduced in tone. Thus ifit is desired to reduce the tone at the top of the tree a positive strip 9 is placed thereon, as shown in Fig. 1.

Engravers plates, namely, the key plate, blue plate, red plate and yellow plate, are now finished in the usual manner with engravers plates used in half tone processes. A picture is reproduced by printing the colors over one another. The final reproduction resulting from printing the colors over one another shows the reproduced picture in all the natural color effects. This process also gives the natural light and shade effects without the use of an shading screen process. As one negative is used throughprocess all the plates will register perfectly.

In processes wherein pigment has been directly applied to the surface of the half tone negative, the following occurs: Pi ment must be applied thereto in relative y roperly stop out portions of he r s t is hat when the the negative.

said film upon said half tone naeaooa transfer is made to the engravers plate, wherein the film is placed in close contact with the plate, parts of the filmnot covered with pigment are spaced such a distance from the plate as to cause difi'usion of light and blurring.

What I claim is:

l. The process of making engravers plates, which comprises producing a half tone negative; producing a transparent .film by placing a sensitized vehicle upon a plate, treatingthe unexposed plate so formed with a fixin agent, treating said plate with a composition to produce a flexible film, stripping the film from said plate, superimposing negative with the side which was next to the plate outward to'produce a tracing negative; stopping out thereon with removable pigments portions other than selected colors to produce a color a negative; and printing therefrom on an engravers plate.

2. The process of making engravers plates, wh1ch comprises producing a half tone negative; producing a transparent film by placing a sensitized vehicle u on a plate,

treating the unexposed plate so ormed with a fixin agent, treating said plate with a composition to produce a flexible film, stripping the film from said plate; superimposing said film upon said half tone negative with the side which was next to the plate outward to produce a tracing negative;

stopping out thereon with removable pigments portions other than selected colors to I produce a color negative; printing thereblack and white negative with light tones from on an engravers plate; and restoring said tracing negative by removing said pigment.

3. The process of making engravers plates for photoengraving, comprising pro ducing a half tone negative; producing a of the picture eliminated therefrom; superimposing said black and white negative and said half tone negative, thereby providing a key negative; printing from said key negative on an engravers plate for producin a key plate, stripping said black and white negative from said half tone negative; producing a transparent film by pressing a sensitized vehicleupon a plate, treating the unexposed plate so formed with a fixing agent, treating the plate with a composition to produce a flexible film, stripping the film from said plate; superimposm said film upon said half tone negative wlth the side which was next to the plate outward to produce'a tracing negative; stopping out there: on with removable pigment portions other than selected colors to produce a color negative; and printing therefrom on an engravers plate to produce a color plate.

4. The process of making engravers plates for photoengraving, comprising producing a half tone negative;

sensitized vehicle upon a plate, treatin the unexposed plate so formed with a xing agent, treating the plate with a composition to produce a flexible film, stripping the film from said plate; superimposin said film upon said half tone negative with the side a which was next to the plate outward to prov roducing a black and white negative with-l1ght tones of duce a tracing negative; stopping out there- 'on with removable pigment portions other than selected colors to produce a color nega tive; printing therefrom on an engravers plate to produce a color plate; and restoring said tracing negative by removing said pigment. I y

In witness that I claim the foreoing T have hereunto subscribed my name tis 11th day of July, 1916. 1 

